1. Field of the Invention
The present invention relates generally to receivers, and more particularly, to a receiver with equalization.
2. Related Art
A conventional receiver includes multiple receiver components, some of which may be used to overcome signal impairments. Some of the components may implement a carrier tracking loop. The carrier tracking loop tracks differences between transmit and receive carrier frequencies and/or phases. Because a carrier tracking loop having a short loop delay is usually considered to have better performance than a loop with a long loop delay, it can be beneficial to close the loop closer to an end of the receiver. However, this arrangement can result in an undesirable interaction between the tracking loop and other receiver components. Thus, the arrangement can disadvantageously reduce the effectiveness and/or adaptability of some or all of these other receiver components. This may disadvantageously increase receiver acquisition time and reduce receiver Signal-to-Noise ratio (SNR) performance. There is a need therefore for a receiver arrangement that overcomes these disadvantages.
An embodiment of the present invention is a receiver including a filter stage including one or more adaptive and/or static pre-filters, a carrier loop, and an equalization loop. The equalization loop includes an adaptive equalizer. The present invention decouples an interaction between the carrier loop, the pre-filters, and the equalizer using a technique referred to as xe2x80x9cremodulation.xe2x80x9d The architecture of the present invention is more stable and significantly faster than conventional architectures. For example, the present invention improves receiver acquisition time and SNR performance compared to conventional receivers.
An embodiment of the present invention is a receiver for processing a received signal, the received signal includes symbols and a frequency offset from baseband. The receiver includes a carrier tracking loop for generating an estimate of the frequency offset. The receive includes a filter stage for filtering the received signal to produce a filtered signal, whereby the filter introduces inter-symbol interference (ISI) in the filtered signal. A converter converts the filtered signal to a baseband signal that is substantially free of the frequency offset and the ISI, responsive to the frequency-offset estimate and a restorative signal that compensates for the ISI. A detector detects the symbols in the baseband signal to produce a decision signal. A restorative signal generator generates, from the decision signal, the restorative signal responsive to the frequency-offset estimate, such that the restorative signal compensates for the ISI. The restorative signal generator is referred to as a decisional feedback equalizer (DFE) with remodulation. Further embodiments of the present invention are described below.